1. Field of the Invention
The present invention is related to climbing aids and more particularly to mechanically expanding climbing aids which lockingly engage cracks in rock and function as a firm and secure anchor in order to protect climbers by either preventing or arresting a fall.
2. Description of the Prior Art
Climbers typically utilize rope along with a variety of mechanical devices which aid and protect their movement over a rock face. Some of the climbing aids serve as a means to firmly anchor the rope, and thereby the climber, to the rock for the purpose of either preventing or arresting a fall.
A firm and secure anchor can sometimes be accomplished by wedging a climbing aid of fixed shape into a crack in the rock. Such fixed shape climbing aids are known in the climbing community as chocks or chockstones or nuts. They are available in a variety of shapes and sizes in order to accommodate variations in the shape and size of the cracks which a climber may encounter.
U.S. Pat. No. 4,082,241, entitled Chock for Mountain Climbing, issued to John Brent Burkey on Apr. 4, 1978, teaches a chock for mountain climbing which is in the form of a truncated pyramid. U.S. Pat. No. 3,948,485, entitled Irregular, Polygonal Mountaineering Chock, issued to Yvon Chouinard and Thomas M. Frost on Apr. 6, 1976, teaches a polygonal chock. U.S. Pat. No. 4,069,991, entitled Chock for Rock Climbing, issued to Thomas C. Saunders and James R. Clark on Jan. 24, 1978, teaches a chock for use with a loop sling. U.S. Pat. No. 3,946,975 entitled Climber's Chockstone, issued to Thomas G. Lyman, Jr. on Mar. 30, 1976, teaches a chock which is formed of a polycarbonate resin defining a body having three different sized pairs of opposed faces. U.S. Pat. No. 4,422,607, entitled Climbing Chocks, issued to Mark Vallance on Dec. 27, 1983, teaches a chock having a generally wedge shaped body with two opposite side faces of which are respectively of concave and convex configuration.
Climbing aids of a fixed shape and size are not very effective in wide, smooth, parallel sided or openly flaring cracks. For such applications, mechanically expanding climbing aids have been developed. U.S. Pat. No. 3,877,679 entitled Anchor Device for Mountain Climbers, issued to Greg E. Lowe on Apr. 15, 1975, teaches a climbing aid which includes a main body and an orientation assembly. The orientation assembly is pivotally mounted on the main body and provides the means for attachment of the climber's rope. The main body is provided with opposed pairs of tapered sides forming wedges for fixed size placement in cracks. In addition, the main body has an arcuate cam surface which is configured to spiral outward with a constant surface intercepting angle as it rotates about the orientation assembly pivot point.
U.S. Pat. No. 4,184,657, entitled Climbing Aids, issued to Raymond D. Jardine on Jan. 22, 1980, teaches a climbing aid which includes a support bar, a single spindle which is mounted on the support bar, two pairs of cam members which are pivotally mounted on the spindle and which are adapted for opposite pivotal movement from a "closed" position to an "open" position, and spring members which are mounted on the spindle between each pair of cam members and which act to apply force to each cam member in order to urge them into their "open" positions. The climbing aid also includes an operating bar which is slidably mounted on the support bar and which is connected to each cam member. A climbing rope attachment point is located on the support bar at the end opposite the spindle. A downward force on the operating bar pulls the cam members into their "closed" positions so that the climbing aid can be inserted into a crack. The operating bar is then released and the spring members force the cam members toward their "open" positions in order to hold the climbing aid within the crack. The cam members are shaped such that movement progressively spirals the cam surfaces outward thereby jamming the climbing aid within the crack.
U.S. Pat. No. 4,491,291, entitled Climbing Aid for Mountain Climbers, issued to Paul W. Ching on Jan. 1, 1985, teaches a climbing aid which includes a pair of laterally extending plates and a load bearing member. The plates frictionally engage facing surfaces of a crack in order to preclude withdrawal from the crevice of the supported load bearing member. The climbing aid also includes a release which is located on the load bearing member and which, on actuation, retracts the plates in order to accommodate withdrawal of the climbing aid from within the crack.
The mechanically expanding climbing aids of U.S. Pat. No. 3,877,679, U.S. Pat No. 4,184,657 and U.S. Pat. No. 4,491,291 have several shortcomings which limit their reliability and consequently their usefullness. High jamming forces, which are generated when a load is applied, are directed to and concentrated at the ends of a single, relatively long shaft, which can lead to structural failure due to bending. Spaced, staggered mounting of opposing cam members on a common shaft produce high bending couples, which also can lead to structural failure. Pivoting cam members on a common shaft necessitates a relatively tight cam surface curvature which concentrates frictional forces over a small contact area, which causes rapid cam surface wear. Some loading situations force the application of side loads which act to bend and break the rigid components of the climbing aid, thereby leading to potentially catastrophic failure. Also, although the climbing aid expanding members typically swing through a 90.degree. arc from the fully retracted to the fully expanded positions, only the central 45.degree. arc of movement is practical for use, thereby requiring a relatively large number of climbing aid sizes in order to accommodate the full range of crack widths which a climber encounters while climbing.